(1.)Field of the Invention
This invention relates to transhexahydroterephthalic acid ester derivatives, and more particularly to transhexahydroterephthalic acid ester derivatives usable as liquid crystals and as an additive to liquid crystal compositions.
(2.) Description of the Prior Art
Nematic liquid crystal substances are widely utilized as electro-optical display elements and the like for their characteristics of changing the optical properties markedly under the influence of an electric field.
In order to actually utilize these substances for an industrial purpose, they should meet several requirements which include: colorless and transparent properties; electrical, optical and chemical stability; wide liquid crystal range desirably from -5.degree. C. to +65.degree. C.; and low viscosity desirably lower than 50 cp.
Although great many liquid crystal substances have been known to date, none of them can satisfy the above-mentioned requirements as a single substance. Therefore, it has been the conventional practice to use for liquid crystal display elements a composition containing two or three or more liquid crystal substances.
In order to impart satisfactory contrast on application of a given voltage, the liquid crystal is required to have predetermined dielectric anisotropy. However, in a case where a conventional high temperature liquid crystal is added to a liquid crystal composition for the purpose of broadening its liquid crystal range, difficulties are encountered in that the properties of the liquid crystal composition are deteriorated by an increase of viscosity or degradation of dielectric anisotropy.